Automatic switch-over signal for telephones



F. A. LEIBE ETAL AUTOMATIC SWITCH-OVERSIGNAL FOR TELEPHQNES.

March 5, 1946.

' INVENTORfi Filed May 1, 1943 llllllllIlL Patented Mar. 5, 1946AUTOMATIC SWITCH-OVER SIGNAL FOR TELEPHONES Frank A. Leibe, Quakertown,Pa., and Walter A. Minor, J 17., New-York, N. Y., assignors to FederalTelephone and Radio Corporation, New York,

N. Y., a corporation of Delaware Application May 1, 1943, Serial No.485,314

15 Claims.

This invention relates to telephone systems of the type in which areceiver and a transmitter at one end of a telephone line arealternately switched into operation, an arrangement especially suitablefor field telephones. In systems of this type it is desirable to providesignaling means for indicating the end of transmission and the switchingof the set from transmitting to receiving position so that the otheroperator will be advised that he can commence transmission. Theinvention is particularly adapted for use in systems employing vacuumtube amplifiers at each end of the line.

The general object of the invention'is to provide a novel switch-oversignal of the indicated type, and specifically a signal that may be usedwith arrangements in which the amplifier as a whole can be connectedeither to the transmitter or to the receiver.

A feature of the invention includes an arrange-- ment' employing apositive feedback circuit in the amplifier arranged for connectionduring a brief signal period to generate signal-producing oscillationsin the amplifier circuits. A specific purpose is the provision ofautomatic means "for connecting and disconnecting such feedback circuit,operative when the set is switched from transmitting to receivingposition. i A further feature comprises the use for this purpose of aswitching arrangement including an automatic timing device such as atime delay unit or a circuit having a predetermined time constant whichregulates the duration of-the signal. Another feature is the utilizationof a unitar switching arrangement for controlling both the transfer ofthe set connections between transmitting and receiving positions and theactuation of the feedback circuit during a signaling period;

Other objects and advantages will appear from the following descriptionconsidered in connection with the accompanying drawing, in which acircuit embodying the invention is diagrammatical'l illustrated.

The disclosed embodiment comprises a conventienal transmitting andreceiving handset In including a receiver l I connected by lines 12 andi3 across a section of an induction coil I4, with the usual blockingcondenser I5 in line I2, and a transmitter microphone It connected bylines I3 and Il across another section of coil I4, with a push-to-talkswitch 58, battery I9, relay 43 and bypass condenser 20 in line H.

The handset is is coupled to a vacuum tube amplifying system'23 byswitch means 24 arranged to connect the amplifying'system between Thehandset I0 is coupled to the amplifying system 23 through a-transformer26 having a coil 21 connected across induction coil I4 and condenser I5,andinductively associated coils 28 and 29 connected to the output andinput respectively of the amplifying system 23 through switch means 2t.Line 25 is connected to the amplifying system through transformer 3E|having coil 3I- connected across the line and coils 32'. and 33connected to the input and output respectively ofthe amplifying systemthrough said switch means. Coil 29 of transformer 2-6 is connected atone end to groundand at the other end to contact 35 of double throwswitch 36 which is connected to the input of the amplifying system 23,the output of which is connected through contact 31 of double throwswitch 38'andline ,39 to one end of coil 28, the other end beingconnected to a source of positive potential providingamplifier tubeanode current. Coil 32 of transformer 3ll'is' connected at one end'tog'roundtand at the other end to contact '40 of switch 36; contact 4| ofswitch 38 being connected to'coil 33 of transformer 30, the other end ofwhich is connected to a source of positive anode potential.

It will be apparent that with this arrangement the simultaneousoperation ofswitches I8, 36 and 38'wi1l' switch the handset I0 andamplifying systom 23 between receiving andtransmitti'ng positions. Asuitable arrangement for simultaneous operation of these switchesis'provided, the form illustrated employing'a relay arrangement. Thelatter includes a primary relay 43' connected across condenser 20 andenergized by battery I9 when switch I 8 is closed. A normally openswitch, 44 actuated by relay 43 is in circuit between the groundedwinding 45 of secondary relay 4,6 and resistance 48 connected to asuitable grounded source of positive potential for energizing relay 45.The latter relay operates switches 36 and38, which are normall held inreceiving position indicated in full lines, but are shifted totransmitting position, indicated by dotted lines, when relay 45 isenergized by the closing of switch 44 due' to the energizing of relay 43through the closing of switch I8. The portion of switch means 24 thusfar described will therefore operate to switch the amplifying system 23automatically between receiving and transmitting positions when thehandset I is similarly shifted by switch 18.

In the particular amplifying system illustrated, employing two vacuumtubes 50 and 5|, switch 36 is connected to control grid 52 of tube 50,said grid and cathode 53 being appropriately connected to provide thenecessary potentials. Cathode 53 is connected through grid biasresistance 56 to ground, and anode 5'! is connected through a suitab eresistance 58 to a source of positive potential.

The output circuit of tube 50 is suitably coupled to the input circuitof tube 5|. In the illustrated arrangement anode 21! is connectedthrough coupling condenser 6| to control grid 62 of tube 5| and theusual resistor 53 to ground. Cathode B5 is connected through the usualgrid bias resistor 66 and bypass condenser 81 to ground. Anode 68 isconnected through line 69 to switch 38.

A negative feedback arrangement may be provided to improve the operationof the amplifying system 23, the illustrated embodiment utilizing fortransmitting a circuit through line 10, including condenser H andresistance 12, c nnecting contact 4! of switch 38 with cathode 53 oftube 50, and for receiving, a circuit from l ne 35 through line 13,including condenser Ma and resistance Mb, to an adjustable connection toresistance 58 which provides again control.

The signaling means is arranged to couple the output and input circuitsof amplifying system 23 so as to produce oscillations when the handsetI0 is switched to receiving position, such oscillations when sent outover line 25 being appropriate to produce an audible signal in thereceiver at the other end of the line. Anarrangement is alsoadvantageously included for terminating such coupling after apredetermined period and thereby limit the signal length. An automaticconstruction for this purpose is disclosed.

In the illustrated construction a signal circuit is introduced by switchmeans into amplifying system 23 when switch i 8 is closed, and isautomatically disconnected after a relatively brief signal period. Theform shown employs a feedback circuit connecting anode 68 of tube 5| andthe control grid-cathode circuit of tube 50. It includes a connection toline 69 through contact 16 of switch TI, and extends through condenser78 and resistance 13 in line 80, to line 39, which is connected towiding 28 of trasformer 26. inductively coupled to winding 29 connectedthrou h contact 35 of switch 36 to grid 52 of tube 55. Switch 11 isnormally closed and is onened by relay 43 when the latter is energized.It therefore remains'open during transmission but is closed whenpush-to-talk switch I8 is opened.

Means is provided for hold n switches 36 and 38 in transmitting positionduring a brief signal period followin the opening of switch l8 and theclosing of fe dback switch 71, so that the feedback circuit 15 mayoperate to produce the signal osc llations. For this purp se a suitablearrangement is employed for keeping secondary relay 4B in operationafter the opening of the circuit of primary relav 43 has resulted in theopening of sw tch 44. While this maybe accomplished in different ways,such as the use of a relay having mechanical means for delaying switchaction, or a time delay circuit employing a vacuum tube, a sim learrangement is disclos d. comrrising a condenser 8| shunted acrosswinding 4.5 Q? r la 46 and having the characteristics necessary tomaintain on said winding a sufiiciently high potential to keep switches36 and 38 in inner or transmitting position during a signal period theduration of which is determined by the ratio at which the charge oncondenser 8| leaks off. The signal duration may therefore be regulatedby the selection of a suitable condenser.

While a preferred embodiment has been illustrated and described, theparticular arrangement disclosed hasbeen set forth for purposes ofexemplification of the invention and not by way of limitation, since itmay be modified without departing from the invention, the scope of whichis indicated by the claims.

What is claimed is:

l. A telephone transmitting and receiving unit including a transmittingcircuit, a receiving circuit, a vacuum tube amplifying system associatedwith the transmitting circuit, switch means for placing said circuitsalternately in operation, means including a feedback signal circuitarranged for connection to the amplifying system to produce signalingoscillation of a singing character and ephemeral duration therein, andsignal control means including a time delay circuit for placing saidsignal circuit means out of operation after a predetermined period oftime.

2. A telephone unit as set forth in claim 1', including switch means forchanging th connections between the amplifying system and thetransmitting and receivin circuits, said switch means actuating thesignal control means.

3. A telephone unit as set forth in claim 1, in which said signalcircuit is arranged to provide oscillation-producing feedback betweenthe output and the input of the amplifying system.

4. A telephone unit as set forth in claim 1, in which the amplifyingsystem includes negative feedback when talking and the signal circuitincludes means for producing positive feedback in the amplifying systemfor a predetermined period of time only.

5. A telephone transmitting and receiving unit including a transmittingcircuit, a receiving circuit, a vacuum tube amplifying system, switchmeans for coupling the amplifying system alternately to the transmittingand receiving circuits, a signal circuit arranged for connection to theamplifying system to produce regenerative signaling oscillationstherein, and signal control circuit means including a relay for placingsaid signal circuit out of operation after a predetermined period oftime.

6. A telephone unit a set forth in claim 1, in which the switch meansincludes an operating switch and intermediate switch means controlledthereby arranged to connect the amplifying system alternately to thetransmitting and receiving circuits, switch means actuated by thecontrol switch for connecting the signal circuit to the amplifyingsystem when the control switch is shifted from transmitting to receivingposition, and time delay circuit means for maintaining said intermediateswitch means in transmitting position during a signal period followingsaid actuation of the operating switch.

- 7. A telephone transmitting and receivin unit including a transmittingcircuit, a receiving circuit, a vacuum tube ampl fying system, switchmeans for coupling the amplifying system alternately to the transmittingand receiving circuits including a connection changing switchconstruction. a relay controlling said switch construction and a masterswitch controlling therelay, a feedback signal circuit arranged forconnection to the amplifying system to produce signaling oscillations ofsinging type and having a predetermined duration therein, and signalcontrol meansfor placing said signal circuit in and out of operationincluding a control switch connecting the signal circuit to theamplifying system, means controlled by the master switch for actuatingthe control switch arranged to close the control switch when the masterswitch is shifted to receiving position, and time delay circuit meansfor holding the relay-controlled switch construction in transmittingposition during a signal period after the master switch is shifted toreceiving position.

8. A telephone unit as set forth in claim '7, in which the switchholding means comprises means for maintaining an energizing. potentialon the relay for a predetermined period after the master switch isshifted to receiving position.

9. A telephone unit as set forth in claim 7, including relay meanscontrolled by the master switch for actuating said relay and the signalcircuit control switch.

10. A telephone unit according to claim 5, including connectionsextending so that the switch for changing the connections between saidamplifying system and said transmitting and receiving circuits,respectively, also controls a relay which in turn actuates the signalcontrol device.

11. A telephone unit according to claim 5, also including connectionsextending so that the circuit of the signal producing device is arrangedto provide oscillation-producing feedbacks between the output and theinput sections of said amplifying system. 7

12. A telephone unit according to claim 5, also including connectionsextending so that the amplifying system includes means for yieldingnegative feedbacks, the signal circuit include connections for producingpositive feedback in said amplifying system, and the positive feedbackis sufficiently great to overcome the effect of said negative feedback,so that the system will oscillate only when said positive feedback isconnected into the circuit.

13. A telephone transmitting and receiving unit according to claim 5,also including two relays and connections extending so that said switchis arranged to couple said amplifying system alternately to thetransmitting and receiving circuits, said signal producing circuit isarranged for connection to the amplifying system for only a briefinterval, at the time of change-over, so as taproduce signalingoscillations therein, and said signal control device for placing saidsignal producing circuit in and out of operation, actuates the first ofsaid relays, which latter in turn actuates a second relay, said secondrelay having slow release action.

14. A telephone unit according to claim 5, in which the switch as awhole includes an operating switch and an intermediate switch controlledthereby, and is arranged to connect said amplifying system alternatelyto the transmitting and receiving circuits, so that said switch as-awhole is actuated by operation of the control switch so as to connectthe signal producing circuit to the amplifying system when thechange-over control switch is shifted from transmitting to receivingposition, and also including a slow release relay which maintains saidintermediate switch in transmitting position during a signaltransmission period following the actuation of said operating switch.

15. A telephone unit according to claim 5, includinga slow release relayand in which the switch holding arrangement comprises a capacitativedevice in parallel to the relay winding for maintaining an energizingpotential on said slow release relay for a predetermined period afterthe change-over switch is shifted to receiving position so as to delaythe restoration thereof to inoperative position, after actuating currentis removed from said relay.

FRANK A. LEIBE. WALTER A. MINER, JR.

